A wireless communication network is generally divided into cells which are circular is shape and sized according to the range with which antennas located at a Base Station Transceiver System (BTS), centrally located within the cell, can transmit to and receive from mobile stations without interfering with signals transmitted in adjacent cells. Each mobile station operating within a cell requires a certain amount of bandwidth to operate and, because the total bandwidth of base antennas is limited, the number of mobile stations which can operate within a cell is limited.
To increase the number of mobile stations which can operate within a cell, cells are typically divided into three sectors, each of which sectors cover 120.degree. of the cell. Furthermore, to improve the reception of signals transmitted from mobile stations, two antennas are typically provided for each sector, such that each sector is provided with a total of six base antennas. Of the two antennas, one is a "main" antenna and the other one is a "diversity" antenna. The main antenna both transmits and receives signals to and from a mobile station, while the diversity antenna only receives signals from a mobile station. The diversity antenna is spaced apart from the main antenna to provide "space diversity" so that if one of the two antennas is not able to receive a signal transmitted from a mobile station, which may result from an obstruction in the path of transmitted signal, then the other antenna may receive the signal. A structure for supporting the six antennas for each cell is typically configured as a triangular platform, each side of which supports two antennas for one of three sectors of a cell.
To further increase number of mobile stations which can operate within a cell, cells may be divided into six sectors. There are, however, a number of problems associated with dividing cells into six sectors. For example, a hexagon-shaped (i.e., six-sided) platform configured for supporting twelve antennas with two antennas on each side sufficiently spaced apart to provide diversity would be six times larger than a triangular platform which provides that same space diversity for three sectors. Such a larger platform would cost more to build and install, be more visibly conspicuous, be more susceptible to weather such as wind currents. A larger platform would also weigh more and may also require a stronger mast to support it. While a six-sector platform is being installed to replace a three-sector platform, downtime would also be incurred during which mobile stations in the cell would not be operable. Alternatively, if a smaller platform is used which compromises the space diversity, then signal quality is degraded.
Accordingly, a continuing search has been directed to the development of an antenna structure which would support a six sector cell with acceptable space diversity to maintain good signal quality, but which does not require that a new larger and more costly platform be installed, and possible a new mast also be installed, during which installation wireless communications in the cell would be interrupted.